Furnace control device



Sept. 13, 1938. J, HOUSE 2,130,133

FURNACE CONTROL DEVICE I Filed Oct. 24, 1934 2 Sheets-Sheet l INVENTOR- ATTORNEYS.

Sept. 13, 1938. J. Q. HOUSE 2,130,133

FURNACE CONTROL DEVICE Filed Oct. 24, 1954 2 Sheets-Sheet 2 INVENTOR.

TTORNEYJ.

Patented Sept. 13, 1938 UNITED STATES FURNACE CONTROL DEVICE John Q. House, Cleveland, Ohio, assignor to John H. Leonard, Cleveland, Ohio, trustee Application October 24,

11 Claims.

This invention relates to a damper control mechanism for furnaces and the like, a principal object being to maintain uniform rates of combustion of predetermined intensities.

An equally important object is to modulate and control the admission of air into and the discharge of products from the combustion chamber in a manner such that the heat produced is efliciently applied, overheating of the furnace 1 eliminated, and stack losses of combustible matter and heat are greatly reduced.

Another object is to prevent over checking and consequent extinguishment of the fire.

A more specific object is to provide a simple and durable apparatus for controlling the operation of the furnace, which apparatus has a minimum number of working parts, may be installed readily without material or expensive changes in the furnace structure, and which operates to maintain a rate of combustion commensurate with the amount of heat required and rate of transfer and convection of the heat from the furnace.

Other objects and advantages will become apparent from the following specification wherein reference is made to the drawings, in which Fig. 1 is a diagrammatic side elevation of a furnace showing an exemplary installation of the present invention;

Fig. 2 is a top plan view of a damper mechanism embodying the present invention, the check damper being partially broken away for clearness in illustration;

Fig. 3 is a vertical sectional View of the control damper and operating 'mechanism and is 35 taken on a plane indicated by line 33 on Fig. 1;

Figs. 4 and 5 are sectional views taken on planes indicated by the lines 44 and 5-5 respectively of Fig. 2; and

Fig. 6 is a diagrammatic illustration of the 40 electrical circuits and vapor motor which may be used in connection with the damper mechanism, the vapor motor being shown in section for clearness in illustration.

For the purposes of illustration, the invention is shown in connection with a generally used type of household hot air furnace, its use with other types of fuel burning equipment being readily apparent therefrom.

Referring first to Fig. 1, the furnace comprises 50, a combustion chamber C, enclosed in the usual air jacket J, and having a discharge flue F which communicates with a suitable stack S, the stack forming a continuation and part of the flue F and the extending portion F of the flue being provided with the usual adjustable check damper D 1934, Serial No. 749,705

which, in the present invention, is kept closed at all times. An adjustable inlet damper I for controlling the admission of air to' the combustion chamber through the ash door is also provided.

It is well known that in the usual furnace, if operating with the check damper D closed and the inlet damper I open, the rate of combustion of the fuel will increase rapidly until the exhaust flue F and the stack S are unduly heated, due both to the direct escape of heated products from the combustion chamber and to the combustion in the flue and stack of volatile gases carried thereinto. After a predetermined. high temperature of the combustion chamber is reached, air cannot pass through the jacket J around the combustion chamber rapidly enough to absorb the heat as rapidly as it is being pro-. duced. Consequently, a large percentage of the heat is lost, the furnace and flue are overheated, and the discharge of heated air into the room does not increase in an efficient ratio to the intensity of the heat of the furnace.

In order to control the furnace so as to overcome these disadvantages and to check the fire when the flue gases have reached atemperature at which radiation of heat from the radiating hood and combustion chamber of the furnace is efficient in relation both to the passage of air thereabout and to the temperature requirements of the rooms to be heated, the control mechanism of the present invention is provided. Referring to Figs. 2 to 5 inclusive, the control mechanism comprises a butterfly flue damper Ill having a central bleeder vent I l and mounted on a radially protruding shaft l2. The damper H] is preferably of such size that, when turned to dispose the plane of its surface transversely of the flue F or portion of the stack in which disposed, it substantially fills the flue and blocks the same except for the vent II and leakage around its margins. The shaft I2 is rotatably mounted in the wall of the flue F and protrudes outwardly therefrom. Adjustably secured on the outwardly protruding end of the shaft I2 is a yoke having arms I3a and I32), which preferably extend horizontally and are disposed generally in a plane through the axis of the shaft I2 and 45 to the plane of the damper l0.

Mounted on the flue F is a housing M in which is rotatably mounted a horizontal shaft l5, which extends parallel to the flue F. The housing I4 is disposed between the damper l8 and stack S, the end of the shaft l4 nearest the damper protruding through the end wall of the housing. The

protruding end of the shaft I5 is provided with a tongue |6 disposed at to the shaft axis and extending between the arms |3a and I3!) of the yoke. Thus rotation of the shaft |5 through about 90 swings the damper ID to open and closed positions. For adjustment, the tongue may be secured on the shaft |5 by a collar |6a and set screw |6b. Secured by one end to the shaft l5, within the housing I4, is a thermostatic bimetal coil I1.

In one end wall of the housing I4 is a vertical slot |8 through which an anchor lug l9 protrudes so that it may be moved along the slot from outside the housing. The lug is provided with a bolt |9a which is engaged by a wing nut IS?) on the outside of the housing for securing the lug in different adjusted positions. The opposite end of the thermostatic coil I1 is fixedly secured to the anchor lug 19. Thus, if the lug is held in a given fixed position, the coil upon heating and cooling, will rotate the damper toward closed and open positions respectively.

The eificiency of convection, the ratio of flue temperatures to hood temperatures, and the rates of combustion desired vary for different furnaces and under different conditions to be met. Consequently it is desirable to adjust the tension on the coil so that it will operate the damper to fully closed and open position within different temperature ranges consistent with such extraneous conditions.

This adjustment of the coil I1 is effected by moving the anchor lug up or down, as the case may be, and securing it in the desired position.

The portion of the housing M which accommodates the coil I1 is preferably partitioned off from the remainder by the partition wall 20a and 20b and the bottom wall 2| of this portion is concave upwardly and deeper than the remainder of the housing so that, when the housing rests upon the flue F, the coil accommodating portion protrudes into the flue and is rendered more quickly responsive to the temperature therein. The remainder of the bottom wall of the housing 4 may be shaped to conform to the shape of the flue on which installed. The bottom wall of the largest portion of the housing |4, between the partition wall 20a and the opposite end, is provided with an opening 22, a coextensive opening being provided in the flue F so that air may pass through the housing to the flue to check the draft. As stated above, the usual check damper D is kept closed at all times. Mounted on top of the housing I4 is a check damper 23 which swings upwardly for opening the passage through the housing and which may return by gravity to closed position.

The coil I1 is such that as its temperature is increased, it rotates the shaft l5 to swing the flue damper ID to closed position, shown in Figs. 3 and 5. It is desirable that the check damper be gradually opened as the damper l0 closes and vice versa. To accomplish this result, a lever 24 is rigidly secured on the shaft I5 in position to engage the underside of the damper 23 and lift the same as the shaft rotates. The relation between the operation of the dampers I0 and 23 with respect to each other and with respect to the coil may be varied by bending the lever 24 to different adjusted positions as well as by shifting the position of thecollar |6a on the shaft l5.

In most instances, however, it is desirable to supplement the mechanical operation of the flue damper ID by electrical operation of the check damper 23 and of the inlet damper I of the furnace. For this. purpose, an electrically responsive motor is provided, an electrically heated vapor motor such as indicated at 25 in Figs. 1 and 6 being preferable.

The shaft l5 extends through the partition wall 201) of the housing I4 and protrudes into the supplemental portion 26 of the housing. On the protruding end of the shaft I5 is a cam 21 which may be secured in different rotated positions relative to the shaft l2 by means of a set screw 28, the operating faces of the cam being covered with insulating material and forming operating abutments for a suitable high and low limit switch mechanism. The switch mechanism, in turn, comprises a high limit spring lever 29 and a low limit lever 30, secured to the wall 201) and suitably insulated therefrom. Each is provided near one end with electrical contactor 29a, and 300, respectively, and both are of electrical conducting material. A common complementary contact element 3| is provided and comprises a block of electrical conducting material which is secured in fixed position on the wall 2% and is insulated therefrom, and carries a contactor 3|a. The levers 29 and 30 are so positioned that in certain rotated positions of the shaft I5, the cam 21 engages them and swings them to break contact, and in other rotatedv positions, disengages them so that they spring back and return the contactors to effect engagement of the contactors 29a and 30a with the common contactor 3|a.

The thermostatic coil is preferably arranged relative to the damper It) so that, at normal room temperatures or a few degrees thereabove, the damper will remain fully open. Upon heating, the coil |1 rotates the damper shaft |5 to close the damper Ill. The cam 21 is usually adjusted so that when the damper I0 is in closed position,

the contact between the contactors 29a, 30a, and

3|a will be broken as shown in Fig. 4. In order that normal tension on the coil I! may be changed by positioning the anchor lug IS without causing it to move the damper l0 beyond its fully closed position when heated, a suitable stop 32 is provided. Upon cooling of the coil H, the cam 2! is rotated counter-clockwise. The longest operating face of the cam 21 operates the low limit control lever 30 and the shorter face, the lever 29, for purposes later to be described.

Referring particularly to Fig. 6, the levers 29 and 30 are connected, through the lead wires 33 and 34 each in separate electrical series with an electric heating element 35, and a step down transformer 36, the common contactor 3|a completing both circuits. The circuits, so described, are preferably of low voltage, the same being energized by the usual volt alternating current household circuit through the medium of the transformer 36.

The heating element 35 is utilized to operate the vapor motor 25, such as diagrammatically illustrated in Fig. 6, which motor is utilized to operate the check damper 23 and inlet damper I. Generally, this motor consists of a closed cylindrical compartment in which is provided a reciprocal piston 38. The lower end of the compartment is contracted as indicated at 39, the contracted portion containing a suitable highly expansive liquid or fluid which, when heated by the element 35, will operate the piston in one direction. A return spring 40 is provided for returning the piston in the opposite direction. The piston, in turn, is connected to a lever 4| which carries an operating lever 42. One end of the operating lever 42 is connected through the medium of a chain 43 and suitably arranged pulleys to the check damper 23, and the other end of the lever 42 is similarly connected to the inlet damper I. When the lever is moved to the position indicated in Fig. 1, the inlet damper I is closed and the check damper 23 opened and when the lever is rotated to dispose it in the reverse position, the check damper will be moved to closed position and the inlet damper I to open position. The piston is so connected to the lever 4| that it moves the lever 42' to position to open the inlet damper I and close the check damper 23 consequent upon heating of the fluid and closes the damper I and opens the check damper I upon cooling of the fluid. Thus any failure in the electrical power supply will immediately check the furnace and eliminate fire hazards due to overheating.

Instead of the vapor driven motor, however, any of the well known types of electrical motors commonly used for opening and closing dampers may be utilized, the circuit thereto being varied to meet the requirements of the particular motor, all in a well known manner.

For most conditions, the normal setting of the thermostatic coil IT is such that it will close'the damper Ill upon reaching the stack temperature of 400 to 450 Fahrenheit.

Since it is generally desirable to control the furnace partially in response to room temperatures, a thermostat 45, described herein as located in the room to beheated, though it may be responsive to heat elsewhere, is provided. The thermostat 45 is of the type to make contact when cool and break contact when heated and is connected in series in circuit with the high temperature limit lever 29.

Therefore, assuming both the room to be heated and the furnace are cool and the fire is started, the room thermostat, being cooled below its set minimum temperature is in position to close the circuit therethrough. The cam 21 is disposed about horizontally and both electrical circuits to the motor through the contactors 29a, 30a and cm are closed and energized. The damper ID is fully open as also is the inlet damper I, the check damper 23 being closed. In this position the entire stack pull is effective for increasing the rate of combustion. The motor continues to maintain this relation while energized. If, while this condition exists, the room reaches the required temperature, the thermostat 45 breaks the circuit and the motor operates to close the inlet damper I and open the check damper 23 unless the low limit switch is closed. Usually, however, the heating of the room lags behind the heating at the furnace and before the roomthermostat breaks contact, the damper It) becomes eifective. Thus with the damper I' open and check damper 23 closed, the entire stack draft is effective and increases as therate of combustion increases. This causes an increase in the temperature of the flue gases and the products passing around the housing l4 and results in heating the coil l1. As the coil I! becomes heated, the damper ID is gradually moved toward closed position, thus reducing the stack pull that is effective in the combustion chamber of the furnace and retaining the gases therein, sufiicient air bleeding in through the fuel bed to maintain combustion of the so retained gases. The lighter products of combustion, however, are bled out around the damper H] and through the passage ll. Meanwhile the low limit switch has been opened.

In the usual furnace, air will not pass through the jacket fast enough to absorb heat efliciently beyond a furnace temperature of about 300 consequently a rate of combustion which increases the temperature unduly beyond 300- disproportionately increases the stack losses. However, as this temperature is approached the damper i0 is closed gradually so as to reduce the increase in rate of combustion and, in fact, maintain a substantially constant rate by reducing the effective stack pull, bailling the heated gases and also volatile matter from escape through the flue or stack and retaining them longer in the combustion chamber.

When the rate of combustion increases too rapidly an over run in the flue temperature results. Likewise a steady, though slower, increase in combustion might continue even with the damper l0 closed. However, when the damper ID has moved to the fully closed position, the abutment cam 21 has engaged the lever 29 and moved it so as to break the contact between the contactors 29a and 3m. This operation renders the coil inoperable by both limit circuits whereupon the motor operates in the reverse direction to lower the damper I and open the check damper 23 thus reducing the intensity of combustion to a degree to which the heat can pass from the furnace.

Upon starting a fresh fire these operations may be repeated several times until the surge in the increase or decrease of combustion is gradually reduced and a comparatively steady fire at the required rate for eflicient radiation is obtained. In this condition the furnace comes primarily under the control of the damper I0 which modulates the rate of increase and decrease to a substantially uniform rate of combustion at the intensity for which the damper ID has been set. However, complete checking for a long period may extinguish the fire, especially on a warm day on which the room thermostat would never close the high limit circuit. However, the cam 21 remains in operative engagement with the lever 30 breaking its contact until a much lower temperature of the coil I1 is reached, for example, a stack temperature of 200 Fahrenheit. At this lower temperature, the low limit circuit is energized to close the check damper 23 and open the inlet damper so as to sustain combustion at a lower rate.

The motor 25 is preferably comparatively slow in operation so that too rapid changes in the operation of the furnace are eliminated.

For purposes of illustration, the damper l0 and operating mechanism have been shown as installed in the stack portion F near the combustion chamber so as to be more quickly affected by changes in the chamber. The structure may, however, be placed directly in the upright or other portion of the stack.

Usually the lever 24 permits closing of the check damper 23 before and effects opening thereof after the temperatures at 'whichthe check will be operated by the motor 25, so it does not interfere with motor operation but supplements it. If many instance, the setting of the high and low limits is such that the lever 24 interferes with the motor operation, the lever 24 may be removed or bent out of place. The contactors 29a and 30a, as well as those of the room thermostat are preferably of the adjustable gap type so that substantially any desired range of high and low limits may be obtained.

It is apparent from the foregoing description that a simple and effective apparatus for the purposes recited is provided, and changes in the structure shown may readily be made without departing from the broad features of the invention. V

I claim: I

1. In a fuel burning apparatus having a combustion chamber, an exhaust flue leading therefrom, an inlet air-control damper and a check damper, a flue damper disposed withinsaid flue and movable to different positions to vary the effective size of the flue passage, thermostatic means responsive to heat of the products in said flue and operably connected to the flue damper for moving the same to said different positions, an electrically operable motor means drivingly connected to one of said first named dampers for moving the same to predetermined positions, an electric circuit connected to said motor means and to a'source of electrical power, and means operable by said thermostatic means for energizing and unenergizing said circuit whereby the flue damper and one of said other dampers are operated in given relations to each other by the thermostatic means and motor means respectively.

2. In a fuel burning apparatus having a combustion chamber, an exhaust flue leading therefrom, an inlet air control damper and a check damper, a flue damper disposed within said flue and movable to different positions for varying the effective size of the flue passage, thermostatic means responsive to heat of the products in said flue and operably connected to the flue damper for moving the same to said different positions, an electrically operable motor means drivingly connected to one of said first named dampers for moving the same to different positions, an electric circuit connected to said motor and to a source of electrical power, abutment means movable by said thermostatic means concurrently with the flue damper, an electric switch in said circuit, and an operating lever thereon movable to different positions tomake and break said circuit, said lever being disposed in the path of travel of said abutment means and movable thereby to predetermined positions for effecting operation of the damper associated with said motor means.

3. In a fuel burning apparatus having a combustion chamber, an exhaust flue leading therefrom, an inlet air control damper and a check damper, a flue damper operatively associated with the flue and movable to different positions for varying the operation of the combustion chamber, thermostatic means responsive to heat of the products in said flue and operably connected to the flue damper for moving the same to said different positions, an electric circuit, electric motor means electrically connected in said circuit and operably connected to the inlet damper for opening the said inlet damper consequent upon energization of said circuit, a

switch in said circuit, and means operable con-1 4. In a fuel burning apparatus having a combustion chamber, an exhaust flue leading therefrom, an inlet air control damper and a check damper, a flue damper disposed within said flue and movable to different positions for varying the effective size of the flue passage, thermostatic means responsive to heat produced by the apparatus operably connected to the flue damper for moving the same to said different positions, an electric circuit, electric motor means electrically connected in said circuit and operably connected to the inlet damper for opening the said damper consequent upon energization of said circuit, a switch in said circuit, and means operable consequent upon movement of said flue damper to position restricting the flue passage to open said switch for breaking the circuit therethrough, whereby the inlet damper may be closed.

5. In a fuel burning apparatus having a combustion chamber, an exhaust flue leading therefrom, and a check damper, a flue damper disposed within said flue and movable to different positions for varying the effective size of the flue passage, thermostatic means responsive to heat of the products in said flue and operably connected to the flue damper for moving the same to said different positions, an electric circuit, electric motor means electrically connected in said circuit and operably connected to the check damper for closing the same consequent upon energization of said circuit, a switch in said circuit, and means operable to move said flue damper to position restricting the flue passage and operative to open the switch and break the circuit therethrough when said means is operated to effect said movement of the flue damper, whereby the check damper may be opened, and means operable consequent upon breaking the said circuit to open the check damper.

6. In a control mechanism for a furnace having a combustion chamber, an exhaust flue leading therefrom, an air inlet control damper and a check damper, a flue damper disposed within said flue and movable to different positions, electrical-1y operable, means operable when energized for operating the first mentioned dampers to given positions, an electric circuit connected to said means, a switch in said circuit, a thermostatic lever drivingly connected to said flue damper for moving the same to different positions in response to temperature changes affecting said thermostatic lever, means operable by the said thermostatic lever for opening said switch, and means for returning said switch to closed position, whereby said dampers may be operated in predetermined relations to each other. Y a

7. In a fuel'burning apparatus having a combustion chamber, an exhaust flue leading therefrom, an inlet air control damper, and a check damper, a flue damper disposed within said flue and movable to different positions for varying the effective size of the flue passage, thermostatic means responsive to heat from said apparatus for operating said flue damper, a, motor operable to open the inlet damper and close the check damper when operating in one direction and operable to close the inlet damper and open the check damper when moved in the opposite direction, an electric circuit connected to said motor, a switch in said circuit, said circuit, when entirely closed effecting operation of the motor to open the inlet damper and close the check damper, means operable by said thermostatic means for opening said switch, and means operable consequent upon opening said switch to operate said motor in the opposite direction.

8. In a control mechanism for a furnace having a combustion chamber and an exhaust flue leading'therefrom, a check damper, a flue damper disposed within said flue and movable to different positions, a thermostatic lever drivingly connected to said flue damper for moving the same to diflerent positions in response to temperature changes aflecting said thermostatic lever, means operated by said thermostatic lever and drivingly connected to the check damper for operating the check damper concurrently with the operation of the flue damper, whereby said dampers may be operated in predetermined relations to each other.

9. The combination with a fuel burning apparatus having a combustion chamber, an exhaust flue leading therefrom, a check damper and a flue damper disposed within said flue and movable to different positions for varying the effective size of the flue passage, of thermostatic means directly responsive to heat from said flue and operable to move both said flue damper and said check damper to open and closed positions in inverse relation to each other.

10. In a fuel burning apparatus having a combustion chamber, an exhaust flue leading therefrom, and a check damper, a flue damper disposed within said flue and movable to difierent positions for varying the efiective size of the flue passage, thermostatic means responsive to heat produced by the apparatus and operably connected to the flue damper for moving the same to said different positions, electric circuits, means including an electric motor means electrically connected in said circuits and operably connected to the check damper for closing the same consequent upon energization of either of said circuits and for opening the same when both circuits are open, a high limit switch in one of said circuits, a low limit switch in the other circuit, means operable consequent upon movement of said flue damper to position greatly restricting the flue passage to open both said switches and break the circuits therethrough, thermostatic switch means in the high limit circuit for making and breaking the high limit circuit independently of said high limit switch, and means operable consequent upon movement of said flue damper to less restricting position to close the high limit switch and to a still less restricting position to close the low limit switch.

11. In a fuel burning apparatus comprising a combustion chamber, an exhaust flue leading therefrom and a stack leading from said exhaust flue, a housing mounted on said exhaust flue between the combustion chamber and stack, said exhaust flue and housing having aligned openings communicating the interior of the flue and housing at a point between the combustion chamber and stack, said housing having an opening for admitting outside atmosphere therethrough into the flue, a check damper carried by the housing and cooperating with said last mentioned passage, a flue damper in said flue between the housing and combustion chamber, thermostatic lever means carried by said housing in heat exchanging relation with said flue, and means operated by said thermostatic lever means for controlling said dampers.

JOHN Q. HOUSE. 

